Adsorbents, photoresponsible

The surface of a carbon electrode was at first coated with a thin film of an anionic polymer such as sodium poly(styrene-sulfonate) 95) or nafion 96) (thickness thousand A) then the cationic Ru(bpy)2+ was adsorbed in the anionic layer electrostatically. The modification was also made by coating water insoluble polymer pendant Ru(bpy)2 + ( ) from its DMF solution 97). These Ru(bpy) +/polymer modified electrode gave a photoresponse in the MV2+ solution with the Pt counter electrode 95-97) The time-current behaviours induced by irradiation and cutoff of the light under argon are shown in Fig. 28. It is interesting to see that the direction of the photocurrent reversed at the electrode potential of ca. 0.4 V (vs. Ag—AgCl) under... 

Typical results are shown in Fig. 44. The spectral threshold of the proper photoconductivity and the photo-emf of PAC is situated at 520 nm. The spectral response for the photo emf of PAC itself is shown by curve 1. After PAC has been immersed in an ethanol solution of methylene blue and dried its spectral response is represented by curves 2 and 2. The photo-response appears in the range of the absorption maximum of the dye at 680 nm characteristic of the monomolecular form in the dilute initial solution (curve 3). The observed enhancement of the second maximum at 620 nm in comparison to the solution spectrum is obviously connected with the presence of dye dimers. The shift of the maximum photoresponse to the longer wavelength by 15 nm relatively to the solution is usually the case for the adsorbed state. The sign of the charge carriers both in the proper and sensitized spectra ranges is positive. As seen in Fig. 44 the adsorption of the dye also markedly changes the proper photosensitivity of the PAC. When the monomolecular form of the adsorbed dye dominates, the... 

Dyes such as erythrosin B [172], eosin [173-177], rose bengal [178,179], rhodamines [180-185], cresyl violet [186-191], thionine [192], chlorophyll a and b [193-198], chlorophyllin [197,199], anthracene-9-carboxylate [200,201], perylene [202,203] 8-hydroxyquinoline [204], porphyrins [205], phthalocyanines [206,207], transition metal cyanides [208,209], Ru(bpy)32+ and its analogs [83,170,210-218], cyanines [169,219-226], squaraines [55,227-230], and phe-nylfluorone [231] which have high extinction coefficients in the visible, are often employed to extend the photoresponse of the semiconductor in photoelectro-chemical systems. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl) complex has also been attempted [232,233]. Because the singlet excited state of these dyes is short lived it becomes essential to adsorb them on the semiconductor surface with... 

On the other hand, this procedure for the self-assembled monolayer formation has a drawback. A monolayer adsorbed on a silica plate surface is subjected to the detachment of CRA-CM molecules more or less in polar solvents such as water and alcohols,since the adsorption stems from the hydrogen bond formation. This problem was overcome by the pretreatment of a silica plate surface with an aminoalkylation silylating reagent to introduce amino residues on the surface. A photoresponsive monolayer of... 

Under potentiostatic conditions, photoinduced heterogeneous electron transfer between specifically adsorbed porphyrins and redox couples confined to the organic phase manifests itself by photocurrent responses. As in the case of dynamic photoelectrochemistry, these photoresponses provide information on the dynamics of heterogeneous electron transfer and recombination processes. In addition, we shall demonstrate that photocurrent measurements can be used to characterise the interfacial coverage of the specifically adsorbed porphyrins as well as their molecular orientation. 

Organoclays based on quaternary ammonium compounds are able to adsorb azobenzene derivatives, which confer to the final product attractive photoresponse properties (229). The azobenzene reversibly changes from trans to cis conformation upon UV irradiation or alternatively under mild heat treatment. Interestingly, the variation of the basal spacing shows that the photoresponse is stable for more than 15 cycles (229). 

Very recently, the application of dye-clay intercalation compounds for the removal of toxic substances from water has been examined (291-293). Organic modification of clays with aliphatic or simple aromatic ammonium or pyridinium ions has been conducted to control the adsorptive properties of dyes for this purpose (294,295). Such dye-clay intercalation compounds therefore can be considered as a new class of adsorbents with additional functions, such as sensing and photoresponsive adsorptive properties. 

A photoresponse cannot be obtained at an electrode which is dipped into the mixed solution of these photoreaction components. When the Ru complex is coated on an electrode as a polymer membrane, however, a photoresponse is obtained at the coated electrode in the presence of in the aqueous phase or in the second polymer layer coated on the top of the Ru complex layer As the Ru complex polymer coating, the Ru(bpy)3" /polystyrene sulfonate adsorbed system, Ru(bpy)3" /Nafion adsorbed system or polymer-pendant Ru(bpy)f (i) was used. The monolayer-coated system composed of a polymer membrane containing the Ru complex and... 

On the other hand, an azobenzene derivative was recently used as a photoresponsive probe to examine photoreactions in constrained media. ,Z-photoisomerization was observed over the temperature range of 80 to 300K when a cationic azobenzene derivative, p-((0-dimethylhydroxyethylammonioethoxy)-azobenzene, adsorbed on an aluminum-containing mesoporous silica film as a nano-reactor for photoreactions, was irradiated with 350-nm light. The results indicated that mesoporous silica films can be exploited as a nano-reaction vessel over a wide temperature range for photochemical reactions. 

Table 2 Photoinduced Change in the Capacity of Proteins to be Adsorbed onto a Photoresponsive Polymeric Adsorbent at 25°C ...

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